The present invention relates to a digital filter and, more particularly, to a digital filter for reducing noise in an input signal in a device for measuring a signal of a very low level.
When quantitative analysis of a sample is performed, a chromatograph has been widely used because material composition analysis and its quantitative analysis can be economically performed with a relatively simple operation. The limitations of chromatographic capacity for analyzing a sample of a very low level are determined by a noise component included in an input signal. This noise may be reduced by a filter. However, a frequency band used in the chromatograph falls within the range of 10 Hz to 10.sup.-3 Hz. a conventional filter used at such low frequencies cannot satisfy characteristics required by the specifications of the chromatograph.